Stain-resistant polyamide composition and fibers

ABSTRACT

An acid dye stain-resistant fiber-forming polyamide composition comprising a fiber-forming polyamide and a reagent, at least a portion of which associates with free acid dye sites in the polyamide, thereby disabling the acid dye sites in fibers formed from the composition from taking up acid dye stains; a masterbatch concentrate for addition to a fiber-forming polyamide to form an acid dye stain-resistant fiber-forming polyamide composition comprising a carrier compatible with the fiber-forming polyamide combined with an amount of the above reagent in excess of that desired in the acid dye stain-resistant fiber-forming polyamide; as well as fibers and articles of manufacture prepared therefrom.

BACKGROUND OF TEE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to stain-resistant polyamide compositionsand fibers and articles of manufacture formed therefrom.

[0003] 2. Description of the Prior Art

[0004] Textile and carpet yarns prepared from polyamide fibers aresubject to staining by a variety of foods, drinks and many othercompositions with which it comes in accidental contact. The uptake ofacid dye stains from, for example, soft drinks, is a particularly vexingproblem for polyamide fibers due to the availability therein of acid dyesites such as amine end groups and amide linkages. Several methods havebeen suggested for enhancing the resistance of polyamide fibers to aciddye stains.

[0005] One approach is to apply a so-called “stain blocker” coating −othe surfaces of polyamide fibers to prevent access to the acid dye sitestherein by the acid dye staining composition. An example of such amethod is illustrated by U.S. Pat. No. 5,145,487 which discloses coatingthe fibers with sulfonated aromatic condensates (SACs). Similarproposals are suggested in U.S. Pat. Nos. 4,680,212 and 4,780,099.

[0006] Another approach is to form the fibers from polyamides preparedby copolymerizing monomers, some of which contain sulfonate moieties.Typical of such systems are those disclosed in U.S. Pat. Nos. 3,542,743;3,846,507; 3,898,200 and 5,108,684.

[0007] U.S. Pat. No. 4,374,641 relates to pigment concentrates madeusing sulfonated polymers as carrier resins including the highlysulfonated polyamides disclosed in U.S. Pat. No. 3,846,507. U.S. Pat.No. 5,236,645 represents an improvement on the invention claimed in U.S.Pat. No. 4,374,641.

[0008] Fibers are generally prepared from polyamides by melt-spinning.Sulfonate-containing copolymers generally have higher melt viscositiesthan non-sulfonate containing copolymers for equivalent relativesolution viscosities which limits the extent of polymerization which canbe achieved in batch autoclave reaction vessels due to the retardationthereby of the rate of polymerization, as well as its hindrance ofeffective discharge of the polymerized melt from the reactor. Inaddition, the presence of sulfonates which have surfactant propertiespromotes excessive foaming during the melt polymerization process,resulting in poor agitation of the reaction mixture and non-uniformityof product.

[0009] Yarns having different depths of color require different levelsof stain protection. Thus, light shaded colors show the presence ofstains more than darker colors. It would be advantageous, therefore, tobe able to provide different levels of stain resistance to polyamidesdepending upon the ultimate yarn color without having to provide aseparate polyamide feedstock for optimum formulation of each color yarn.

[0010] An additional disadvantage associated with sulfonate-containingpolyamide copolymers is that they are generally more difficult to drythan sulfonate-free polyamides due to the hygroscopic nature ofsulfonate groups.

[0011] Polyamides that are topically coated to give stain resistance tothe fiber, e.g., with SACs, have the disadvantage that the topicalcoating is removed during use and maintenance. Gradual removal of thecoating will also occur during cleaning with water and detergents.Fibers used for carpet applications may be regularly cleaned withalkaline-based cleaning agents. SAC topical coatings are easily removedusing these types of cleaning agents. The topical coating will also begradually removed during normal wear of the fiber in its chosenapplication. In addition to their removal during use and maintenance,SACs generally have inferior resistance to light, oxides of nitrogen,and bleach, the latter of which is commonly used for the cleaning ofindustrial textiles and carpets. Also, the base color of SACs is notcolorless and thus may change the shade of the color of the yarn.

[0012] It is an object of the present invention to provide a novel andhighly advantageous approach for imparting stain resistance to fibersformed from polyamides.

SUMMARY OF THE INVENTION

[0013] The above and other objects are realized by the presentinvention, one embodiment of which comprises an acid dye stain-resistantfiber-forming polyamide composition comprising:

[0014] a. a fiber-forming polyamide; and

[0015] b. a reagent at least a portion of which associates with freeacid dye sites in the polyamide, thereby disabling the acid dye sites infibers formed from the composition from taking up acid dye stains.

[0016] Another embodiment of the invention relates to a masterbatchconcentrate for addition to a fiber-forming polyamide to form theabove-described acid dye stain-resistant fiber-forming polyamidecomposition, the concentrate comprising a carrier material compatiblewith the fiber-forming polyamide, preferably a polyamide, combined withan amount of the reagent in excess of that desired in the acid dyestain-resistant fiber-forming polyamide such that addition of theconcentrate to the compatible fiber-forming polyamide results in thedesired level of stain resistance.

[0017] An additional embodiment of the invention concernsstain-resistant fibers formed from the above-described polyamidecompositions.

[0018] Further embodiments of the invention comprise articles ofmanufacture prepared with fibers according to the invention such astextiles and carpets.

[0019] A final embodiment of the invention relates to a method offorming acid dye stain-resistant fibers comprising forming a polyamidecomposition according to the present invention into fibers by, forexample, melt spinning.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The terms below have the following meanings herein, unlessotherwise noted:

[0021] “Reagent” refers to any chemical compound, composition ormaterial which associates (as that term is defined below) with the freeacid dye sites in a fiber-forming polyamide to thereby render themunavailable for association with an acid dye, which reagent is incapableitself of associating with or taking up the acid dye.

[0022] “Association” refers to the chemical reaction or bonding betweenthe reagent and the free acid dye sites in the polyamide which resultsin prevention of “taking up” of the acid dye by the polyamide, i.e.,staining. The association may take the form of a chemical reaction or anacid-salt formulation. Additional types of association include hydrogenbonding, dipole-dipole interaction, Van der Waals forces andcoordination complexing.

[0023] “Acid dye stain” refers to any material or composition whichfunctions as an acid dyestuff by reacting with the free dye sites inpolyamides to substantially permanently color or stain the latter.

[0024] The term “acid dye sites” refers to those basic sites inpolyamides (e.g., amine end groups, amide linkages, etc.) which react orassociate with acid dyes, thereby resulting in a stain bonded thereto.

[0025] “Disabling” the acid dye sites from taking up acid dye stainsrefers to the effect of the association between the reagent and the aciddye sites which renders the latter less capable of associating with aciddyes such as, for example, those in soft drinks, tomato-based products,etc., which result in staining.

[0026] The present invention is predicated on the discovery that optimumlevels of resistance to acid dye stain may be imparted to polyamidefibers by compounding certain reagents with fiber-forming polyamidecompositions subsequent to polymerization of the polyamide and prior tothe formation of the fibers. The invention thereby enables avoidance ofthe above-enumerated disadvantages associated with coating the polyamidefibers with stain resistant SACs and with formation of the polyamides bycopolymerizing sulfonate-containing monomers.

[0027] The selection of a suitable non-acid dyeable reagent having atleast one functional group capable of associating with the acid dyesites available in Liber-forming polyamides, thereby rendering those dyesites unavailable for association with acid dye stains, enables theformation of stain-resistant fibers having predetermined and optimumlevels of stain resistance not obtainable by the methods and systems ofthe prior art.

[0028] Suitable such reagents include those having at least onefunctional moiety which preferentially associates with the active aciddye sites in the fiber-forming polyamide and, additionally, contains atleast one sulfonyl group. The reagent, of course, should be otherwisesubstantially inert with respect to the fiber-forming properties of thepolyamide.

[0029] Exemplary of such reagents are those having the formula:

[0030] wherein: Q and Z are moieties which associate with the acid dyesites in the polyamide;

[0031] a is an integer from 0 to 2;

[0032] b is an integer from 1 to 4; and

[0033] R is aliphatic, aromatic or alicyclic.

[0034] The reagent is selected so as to preferentially associate withthe amine end group and/or amide linkage acid dye sites in thepolyamide. Preferably, a substantially colorless reagent is selectedunless, of course, the reagent is expected to contribute a desired colorto the fibers prepared from the polyamide.

[0035] The associative functional moieties, Q and Z, may comprise anychemistry that will associate with amine or amide linkages, providingthat the functionality does not promote increased stain uptake orotherwise deleteriously impact on the ultimate polyamide composition orarticles manufactured therefrom. Thus, Q and Z are preferably combinedto form carboxylic anhydride groups or are, individually, carboxylicacid groups or alkali metal, alkaline earth metal or transition metalsalts thereof; isocyanate groups; epoxy groups; ester groups and a,Bdiketone groups. Thio functionalities are generally not employed due totheir promotion of yellowing in fibers prepared from polyamidecompositions containing them when subjected to light, heat, oxides ofnitrogen, etc.

[0036] The backbone of the reagent or R may be any suitable aliphatic,aromatic, alicyclic or heterocyclic structure such as phenyl, naphthyl,alkyl (straight or branched chain), cycloalkyl including substitutedcycloalkyls, aralkyl, alkenyl and cycloalkenyl.

[0037] Exemplary of such reagents are 5-sulfoisophthalic acid,3-sulfobenzoic acid, 4-(acetoacetamido)benzene sulfonic acid,4-isocyanatobenzene sulfonic acid, 4-(2,3-epoxypropyl)-benzene sulfonicacid, dimethyl-5-sulfoisophthalate, 3,5-di-(2,3-epoxypropyl)benzenesulfonic acid, 3,5-di-isocyanatobenzene sulfonic acid,3,5-di-(acetoacetamido)benzene sulfonic acid, the sodium and lithiumsalts of all of the above, and sodium or lithium salt of sulfophthalicanhydride.

[0038] The invention is applicable to provide acid dye stain resistancein any fiber-forming polyamide such as nylon-6, nylon-66, MXD-6,nylon-11, nylon-12, nylon-69, the amorphous polyamides such as thecopolymer of terephthalic acid and trimethylhexamethylene diamine. Othersuitable amorphous polyamides include nylon-6,I (a copolymer ofhexamethylene diamine and isophthalic acid), terpolymer of lauryllactam,isophthalic acid and bis(4-amino-3-methylcyclohexyl)methane andpolynorbornamide.

[0039] The composition may include any of the conventional adjuvants forenhancing the formation of fibers from the polyamide composition such asanti-oxidants, stabilizers, colorants, processing aids, anti-staticagents, flame retardants, fillers, nucleating agents, anti-microbials,melt viscosity enhancers or mixtures thereof. Catalysts and/or reducingagents can be added to enhance the association of the reagent with thefiber-forming polyamide. Examples of suitable catalysts/reducing agentsinclude salts of hypophosphites such as sodium hypophosphite, ammoniumhypophosphite and manganese hypophosphite, or otherphosphorus-containing organic compounds such as phenylphosphinic acid,polyphosphoric acids and triphenyl phosphite.

[0040] The compositions are prepared by combining the reagent(s),polyamide(s) and, optionally, adjuvant(s) under conditions which ensureassociation between the functional moieties of the reagent and the freeacid dye sites in the polyamide(s). Preferably, the polyamide(s) andreagent(s) are combined by melt blending at temperatures above themelting point of the polyamide(s), but below the decompositiontemperature of the reagent(s). The reagent(s) and polyamide(s) may becombined in a pre-fiber spinning compounding operation or directly inthe fiber melt spinning stage. Product fibers made according to theinvention show durable stain-resistant properties equivalent or superiorto those produced according to the prior art methods without theconsequent disadvantages attendant thereto.

[0041] The reagents (and adjuvants, if any) may be combined with thepolyamide(s) in any suitable form such as powdered, pelletized,encapsulated, etc. The polyamide(s) may be employed as powder, granulesor pellets. The reagent(s) and adjuvant(s) are preferably combined withthe polyamide(s) employing a melt extruder and, most preferably, ascrew-type extruder. Optimally, a twin-screw extruder of the fullyintermeshing type with both screws rotating in the same direction(co-rotating) is employed, although other types of twinscrew extrudersmay be used such as counter-rotating and/or non-intermeshing types.Single screw extruders may also be successfully employed. The extruderpreferably has a barrel length to screw diameter ratio of about 24:1;however, it will be understood that any suitable ratio may be employeddepending upon the parameters of the particular compounding processcontemplated.

[0042] While it is in no way intended to limit the invention by thesoundness or accuracy of any theory set forth to explain the nature ofthe invention, it is postulated that, during the processing step(s), thestain-resistant reagent at least partially associates with, or reactswith, reactive chemical groups or acid dye sites on the polyamide, suchas amine end groups or amide linkages. Removal of volatiles from thecompounding mixture aids this association and/or reaction with thepolyamide. This removal of volatiles is achieved preferably by thepresence of one or more vents on the extruder barrel, although ventingis not a requirement for the process of the invention. When a singlevent is used with an extruder of a length to diameter ratio of 24 to 1,the vent port is suitably located approximately 19 screw, diameters downthe length of the barrel. The optimum position of the vent port isdetermined by the extruder screw profile used. The extraction ofvolatiles through the vent port is preferably vacuum assisted with avacuum level of greater than 10 in. Hg and preferably greater than 20in. Hg. The rate of devolatilization can be assisted throughsubstantially dry nitrogen gas injection through an inlet port locatedeither upstream or downstream of the vent port. Under this situation, alower vacuum level may be acceptable. Additional ways of promoting theassociation and/or reaction with the polyamide are through controlleddrying of the feedstocks, addition of water-scavenging additives, or acombination of these methods.

[0043] The stain-resistant additives and the polyamide resin arepreferably fed to the extruder in a pre-dried form with a controlledmoisture level. The moisture levels of both the additive and the resinare less than 3,000 ppm and are preferably less than 500 ppm. Whendrying both of these materials, an inert gas drying atmosphere ispreferred. The reagent and the resin may be either fed to the extruderas a blend of the two materials using a single feed hopper or by usingseparate feed hoppers of a suitable type such as gravimetric orvolumetric feeders. Additives to enhance the relative viscosity (RV) ofthe concentrate can also be added at this stage. When a blend of thematerials is used, a double cone tumbler blender is preferred forpreparation of the blend, although other types of blenders may be used.

[0044] The extruder temperature profiles used and the desired melttemperature during the mixing process will depend, as noted above,principally on the polyamide type and grade chosen. For example, whenPA6 is utilized, the melt temperature preferred is between 240° C. and260° C. and for PA66 the preferred melt temperature range is between265° C. and 285° C. The optimum melt temperatures for these two resintypes will depend on the grade employed.

[0045] A preferred embodiment of the invention relates to thepreparation of a masterbatch concentrate of polyamide and reagent whichcan be blended with a suitable fiber-forming polyamide prior to or atthe melt-spinning stage to achieve the desired level of stainresistance.

[0046] Only a small proportion of the reagent is reacted with thepolyamide of the concentrate. The bulk of the reagent isdispersed/associated with the resin. It is desired that a proportion ofthe unreacted reagent in the concentrate becomes reacted/associated withthe fiber-forming polyamide. Nylon copolymers are conventionallyproduced via condensation polymerization where water (or other smallvolatile molecule, depending on the chemistry) is generated as aby-product. In order to drive this equilibrium reaction forward, it isnecessary to remove this water by-product from the system below theequilibrium water concentration. If this is achieved in the fiberspinning line, then association/reaction of the unreacted reagent in theconcentrate with the fiber-forming polyamide will occur. In aconventional fiber spinning line, a non-vented extruder barrel istypically used, although vented extruders may be used. The waterconcentration can be reduced to below the equilibrium value by any ofthe methods discussed hereinabove.

[0047] The masterbatch concentrate may be prepared according to themethods described above employing levels of reagent up to about 50% byweight based on the weight of the polyamide.

[0048] Any suitable carrier compatible with the fiber-forming polyamidemay be employed to prepare the masterbatch concentrate. Although it ispreferred to utilize a polyamide carrier, it will be understood that anysuitable polymer, polymer blend or other carrier material which iscompatible with the fiber-forming polyamide may be employed. Suitableother carriers include polyesters and modified polyolefins. Thepolyamide used to prepare the masterbatch concentrate may be the same ordifferent in chemical composition from that of the fiber-formingpolyamide with which the concentrate is combined to produce the ultimatecomposition from which fibers according to the invention are formed.

[0049] When a stain-resistant concentrate or masterbatch is produced,the melt emerging from the die of the compounding extruder is strandedthrough a water batch to solidify the melt, followed by air drying ofthe strand to remove the bulk of the surface water, and pelletization.The concentrate pellets formed are then dried prior to fiber meltspinning to a moisture level of less than 3,000 ppm and preferably lessthan 500 ppm. This drying of the concentrate is preferably accomplishedin an inert gas atmosphere. The concentrate is then mixed on the fibermelt spinning line with non-stain resistant polyamide resin feedstock,dried to a moisture level of less than 3,000 ppm and preferably lessthan 500 ppm, in the desired ratio depending on the level of stainresistance required in the fiber product. The fiber melt spinningprocess of a conventional type is used, familiar to those skilled in theart. Other additives such as colorants and stabilizers may be addedduring the fiber formation process.

[0050] The polyamide resin should have a relative solution viscosity ofequal to or greater than 2.4 and preferably equal to or greater than2.7. The relative viscosity of the resin is determined by firstpreparing 0.55% w/w solutions of the pre-dried polyamide in concentratedsulfuric acid (analytical grade, 96±0.5%). Solution flow times aredetermined in a Cannon-Ubbelhode size 2 viscometer suspended in aviscometer water bath controlled at 25° C.±0.02° C. The flow times ofthe sulfuric acid are also measured. The relative viscosity iscalculated by dividing the flow time of sample solution by the flow timeof the solvent. The polyamide resin should also have an amine end group(AEG) level of less than 60 equivalents per 106 g and preferably lessthan 45 equivalents per 106 g. The AEG level is determined by means of apotentiometric titration. A known weight of sample is dissolved inm-cresol and titrated against 0.1 M perchloric acid in methanol. A blanktitration is also carried out on the m-cresol and used to correct thesample titre.

[0051] In the following examples, a standard test is used to evaluatethe stain resistance of the yarn formed. It involves the use of anacidified solution of FD&C Red 40 dye which is present in the soft drinkcherry-flavored Kool-Aid® commercially sold by Kraft General Foods, Inc.

[0052] Typically, 0.1000 g±0.0030 g of FD&C Red 40 dye (CI Food Red 17)is dissolved in 1,000 cm³ of distilled water. The pH of the dye solutionis adjusted to between 2.80 and 2.90 by making small additions of citricacid of technical grade or better. The pH adjusted solution is allowedto reach room temperature, i.e., 21° C.±1° C., prior to use.

[0053] 1.0000±0.0010 g of yarn is placed in 50 cm³ of the Red 40solution in a 100 cm³ glass beaker and the yarn is briefly stirred inthe solution to ensure that it is fully wetted by the solution. Thebeaker is allowed to stand for 60 minutes without any further agitation.

[0054] The yarn is washed for 120 seconds under free-flowing hot tapwater, that is at a temperature of 40-50° C. The yarn is then dried byinitially blotting with a clean white paper towel to remove the bulk ofthe surface moisture, followed by allowing it to sit at room temperaturefor at least 16 hours.

[0055] The stain resistance of the yarn is determined by visualcomparison to the AATCC Red 40 Stain Scale, which is available from theAmerican Association of Textile Chemists and Colorists (AATCC), ResearchTriangle Park, N.C. The scale consists of ten film squares colored withgradually increasing strengths of FD&C Red 40 numbered from 1 to 10,with 1 being the strongest color and 10 being colorless. The unstainedyarn is placed underneath the colored portions of the scale and thestained yarn is placed underneath the colorless portion of the scale andviewed under daylight or equivalent illuminant. The light should beincident upon the surfaces at an angle of 45°±5° and the viewingdirection should be 90°±5° to the plane of the surfaces. The stainedyarn is compared to the unstained yarn placed under the closest numberedcolored square of the stain scale so that the best color match isobtained. If the color of the stained yarn falls between two squares onthe scale, then half grades are used. The number of this colored square,or squares if the match falls between two squares, is called the StainRating.

[0056] The invention is illustrated by the following non-limitingexamples.

EXAMPLE 1

[0057] A PA66 resin, polymerized from the salt of adipic acid andhexamethylene diamine, with an RV=2.7 and an AEG of 40 equivalents per106 g was dried to a moisture level of less than 500 ppm and tumbleblended with 1.5 wt. % of the lithium salt of 5-sulfoisophthalic acid(LiSIPA), also dried to a moisture level of less than 500 ppm. The dryblend was compounded in a vacuum vented 40 mm twin-screw extruder with alength-to-diameter ratio of 24:1. The screw speed was 249 rpm at athroughput rate of approximately 50 kg per hour. The melt temperature ofthe compound immediately prior to the melt exiting the extruder wasmeasured at 269° C. The vacuum level, as measured directly above thevent of the extruder, was 22 in. Hg. The pelletized product produced wasdried to between 400 and 500 ppm before melt spinning into a fiber of1,850 denier with a filament count of 22 with a trilobal filamentcross-section. The undrawn fiber produced was mechanically crimped at a3.2 draw ratio to give a textured yarn. The stain rating of the yarnusing the standard stain test described above was 5.5. The RV of theyarn was 2.54 with an AEG level of 21 equivalents per 106 g.

EXAMPLE 2

[0058] A PA66 resin with an RV of 3.2 and an AEG level of 27 equivalentsper 106 g was compounded with 1.5 wt. % of LiSIPA, both dried to similarlevels and compounded under similar extrusion conditions as in Example 1above. The measured melt temperature was 274° C. and the vent vacuumlevel was 23 in. Hg. The compound was dried, spun and textured to give ayarn as per Example 1. The stain rating of the textured yarn using thestandard stain test described above was 8.5. The RV of the yarn was 2.50with an AEG-level of 6 equivalents per 10⁶ g.

EXAMPLE 3

[0059] A similar PA66 resin to that described in Example 1, also with anRV=2.7, was tumble blended with 10 wt. % of the sodium salt of5-sulfoisophthalic acid (NaSIPA). The PA66 resin was pre-dried to amoisture level of 380 ppm and the NaSIPA was pre-dried to a moisturelevel of less than 300 ppm. Using the same extruder and similarextrusion conditions, the dry blend was compounded to give a pelletconcentrate. The melt temperature was 269° C. and the vent vacuum levelwas 24 in. Hg. The concentrate was dried to a moisture level of 560 ppmand was blended with the same PA66 resin used to make the concentrate ina 15/85 ratio that was dried to a moisture level of less than 700 ppm.The dry blend was melt spun and textured in a manner similar toExample 1. The textured yarn produced had a stain rating of 5, a yarntenacity of 2.9 g per denier and a % peak elongation of 37%.

EXAMPLE 4

[0060] A similar PA66 resin to that described in Example 1, but with anRV=3.2, was tumble blended with 3 wt. % of LiSIPA. The polyamide resinhad been pre-compounded with copper, iodine and phosphorus containingcompounds with 35 ppm copper, 1,200 ppm iodine and 100 ppm phosphorus.The polyamide resin had been pre-dried to a moisture level of less than700 ppm. The LiSIPA was used in its undried form and had a moisturelevel of 7.0t. The PA66/LiSIPA blend was not precompounded prior tointroduction to the fiber spinning line. The blend was produced into atextured yarn in a manner similar to Example 1. The textured yarn had astain rating of 8 with a yarn tenacity of 3.4 g per denier and a % peakelongation of 48%.

EXAMPLE 5

[0061] A PA6 resin, polymerized from ε-caprolactam without chaintermination, with an RV=2.7 and an AEG level of 35 equivalents per 10⁶g, was dried to a moisture level of 650 ppm. The resin was tumbleblended with 3% of undried LiSIPA. The PA6/LiSIPA blend was compoundedon the same extruder and under similar extrusion conditions to Example 1to give a pelletized compound. The vent vacuum level during compoundingwas measured at 16 in. Hg with a melt temperature of 252° C. Thecompound was dried to a moisture level of less than 1,000 ppm to producea textured yarn in a manner similar to Example 1 using processconditions suitable for PA6 that are familiar to those skilled in theart. The stain rating of the textured yarn produced was 6.

EXAMPLE 6

[0062] A PA6 resin, similar to that used in Example 5 but with an RV=3.3and an AEG level of 27 equivalents per 10⁶ g, was pre-dried to amoisture level of 600 ppm. The resin was tumble blended with 3% ofundried LiSIPA and 1% of undried sodium hypophosphite. The blend wascompounded as per Example 1 with a measured vacuum vent level of 14 in.Hg and a melt temperature of 253° C. The compound was dried to amoisture level of less than 1,000 ppm prior to producing a textured yarnin a manner similar to Example 5. The stain rating of the textured yarnproduced was 8.

EXAMPLE 7

[0063] A PA66 resin similar to that used in Example 2 was compounded ina similar way to Example 2, except that no venting was conducted duringthe extrusion step. Poor strand-ability of the extruded compound wasexperienced. The compound was dried, spun and textured to give a yarn asper Example 1. The stain rating of the textured yarn using the standardstain test described above was 5.5 with an RV of 2.70.

EXAMPLE 8

[0064] A PA66 resin similar to that used in Example 1, but with an AEGlevel of 57 equivalents per 106 g, was processed as described inExample 1. The stain rating of the textured yarn using the standardstain test described above was 4 with an RV of 2.77.

[0065] The feed yarn for manufacture of synthetic textiles and carpetsnormally takes one of two forms: staple or continuous filament. Stapleyarn is produced by spinning an undrawn yarn tow (a large bundle offilaments), that is drawn, mechanically crimped (textured), heat-set andcut into set lengths. The cut yarn is then carded followed by draftingto give a continuous staple yarn. Continuous filament yarn is spun andtextured either as a single process or as a multi-step process. Thefilament bundle size for continuous filament yarn is often considerablysmaller than that used for staple tow. The melt spinning portion forboth staple and continuous filament yarn types is similar, i.e., moltenresin with any desired adjuvants is compounded and fed by a screwextruder or other suitable melting device to a gear pump that forces themelt in a controlled and uniform manner through a melt filtration systemand the fine capillaries in a spinneret, followed by air cooling todriven rolls to carry the fibers away from the face of the spinneret.The melting device used should be designed such that satisfactory mixingis achieved to present a substantially uniform melt to the gearpump/spinneret. The actual design will depend on the resin type andgrade used and the nature of any adjuvants used. The cross-section ofthe capillaries in the spinneret is specifically designed for the fiberend use application and will influence the cross-section shape of thespun fiber. Typical shapes are round, deltoid and trilobal. Varioustypes of texturing processes exist for crimping continuous filamentincluding a stuffer-box, air-jet and false-twist texturing. Drawing ofthe yarn is typically a precursor of the texturing process.

[0066] There are typically three types of methods for forming fibersinto apparel, textiles and carpets: (1) weaving, (2) knitting, includingwarp and circular types, and (3) non-woven techniques, includingtufting. Woven fabrics consist of sets of yarns interlaced at rightangles in established sequences on a loom. Knitting consists of formingloops of yarn with the aid of thin, pointed needles or shafts. As newloops are formed, they are drawn through those previously shaped. Thisinterlooping and the continued formation of new loops produce knitfabrics. Non-woven fabrics consist of a web of staple or filament fibersheld together either by application of a bonding or adhesive agent or bythe fusing of fibers by application of heat. Tufting consists ofinserting loops into an already formed backing fabric. The backingfabric may be of any type and composed of any fiber, including bothnatural and synthetic fibers such as jute and polypropylene. The yarnloops are inserted into the backing with needles. The loops can be cutor left uncut. They are held in place either by applying a specialcoating or by untwisting the tufted yarn and shrinking the backingfabric.

[0067] Fibers of the present invention may be combined into yarnaccording to methods and systems well known to those skilled in the art.Either the fibers or yarns prepared therefrom may be manufactured intonovel textiles, carpets and other articles of manufacture requiringpolyamides having enhanced resistance to staining by acid dyestuffsaccording to conventional, well known methods.

I claim:
 1. An acid dye stain-resistant fiber-forming polyamidecomposition comprising: a. a fiber-forming polyamide; and b. a reagentat least a portion of which associates with free acid dye sites in saidpolyamide, thereby disabling said acid dye sites in fibers formed fromsaid composition from taking up acid dye stains.
 2. The composition ofclaim 1 wherein said reagent associates with acid dye sites comprisingamine groups and/or amide linkages in said polyamide.
 3. The compositionof claim 1 wherein said reagent is substantially colorless.
 4. Thecomposition of claim 1, said reagent having the formula:

wherein: Q and Z are moieties which associate with said acid dye sitesin said polyamide; a is an integer from 0 to 2; b is an integer from 1to 4; and R is aliphatic, aromatic or alicyclic.
 5. The composition ofclaim 4 wherein at least one of said Q and Z is a carboxylic acid groupor a salt thereof.
 6. The composition of claim 4 wherein at least one ofsaid Q and Z is an isocyanate group.
 7. The composition of claim 4wherein at least two of said Q and Z combine to form a carboxylic acidanhydride.
 8. The composition of claim 4 wherein said reagent is5-sulfoisophthalic acid or a salt thereof.
 9. The composition of claim 8wherein said reagent is an alkali metal, alkaline earth metal ortransition metal salt of 5-sulfoisophthalic acid.
 10. The composition ofclaim 9 wherein said reagent is the lithium salt of 5-sulfoisophthalicacid.
 11. The composition of claim 9 wherein said reagent is the sodiumsalt of 5-sulfoisophthalic acid.
 12. The composition of claim 9 whereinsaid reagent is 3-sulfobenzoic acid or the sodium or lithium saltthereof.
 13. The composition of claim 1 wherein said fiber-formingpolyamide is nylon-6.
 14. The composition of claim 1 wherein saidfiber-forming polyamide is nylon-66.
 15. The composition of claim 1wherein said fiber-forming polyamide is MXD-6.
 16. The composition ofclaim 1 wherein said fiber-forming polyamide is nylon-11.
 17. Thecomposition of claim 1 wherein said fiber-forming polyamide is nylon-12.18. The composition of claim 1 wherein said fiber-forming polyamide isnylon-69.
 19. The composition of claim 1 wherein said fiber-formingpolyamide is an amorphous polyamide.
 20. The composition of claim 19wherein said fiber-forming amorphous polyamide is a copolymer ofterephthalic acid and trimethylhexamethylene diamine.
 21. Thecomposition of claim 1 additionally containing a fiber-forming adjuvant.22. The composition of claim 21 wherein said fiber-forming adjuvant isan anti-oxidant, stabilizer, colorant, processing aid, catalyst, filler,nucleating agent, anti-microbial, melt viscosity enhancer or mixturesthereof.
 23. The composition of claim 1 formed by melt blending saidreagent and said fiber-forming polyamide.
 24. A masterbatch concentratefor addition to a fiber-forming polyamide to form the acid dyestain-resistant fiber-forming polyamide composition of claim 1comprising a carrier compatible with said fiber-forming polyamidecombined with an amount of said reagent of claim 1 in excess of thatdesired in said acid dye stain-resistant fiber-forming polyamide. 25.The masterbatch concentrate of claim 24 wherein said carrier is apolyamide.
 26. The masterbatch concentrate of claim 25 wherein saidpolyamide is identical in chemical composition to said fiber-formingpolyamide.
 27. The masterbatch concentrate of claim 25 wherein saidpolyamide is different in chemical composition from said fiber-formingpolyamide.
 28. An acid dye stain-resistant fiber-forming compositioncomprising a fiber-forming polyamide and the master-batch concentrate ofclaim
 25. 29. The composition of claim 28 formed by melt blending saidfiber-forming polyamide and said masterbatch concentrate.
 30. An aciddye stain-resistant fiber or fibers formed from the composition ofclaim
 1. 31. An article of manufacture prepared with the fiber or fibersof claim
 30. 32. A textile article according to claim
 31. 33. A carpetaccording to claim
 32. 34. A method of forming an acid dyestain-resistant fiber or fibers comprising forming the composition ofclaim 1 into a fiber or fibers.
 35. The method of claim 34 comprisingmelt spinning said composition to form a fiber or fibers.
 36. A methodof forming an acid dye stain-resistant fiber or fibers comprisingcombining a masterbatch concentrate according to claim 25 with afiber-forming polyamide compatible therewith and forming a fiber orfibers therefrom.
 37. The method of claim 36 comprising melt spinningsaid combination of masterbatch concentrate and fiber-forming polyamide.